Abstract:A tracking and registration method based on SURF and optical flow in the AR is proposed. The moving object
region is tracked by the optical flow method. This paper extracts and matches the features of the region with SURF because
the algorithm maintains advantages of affine invariance, scale invariance and fast computing speed. The final registration
matrix is calculated using the homographies between adjacent frames. This method reduces the computational time deeply
while the accuracy of the registration unchanges. Convinced by experimental results, this approach can work at almost real
time and achieves accurate registration, and can keep a good robustness in some environment changes.
2024 State of Marketing Report – by HubspotMarius Sescu
https://www.hubspot.com/state-of-marketing
· Scaling relationships and proving ROI
· Social media is the place for search, sales, and service
· Authentic influencer partnerships fuel brand growth
· The strongest connections happen via call, click, chat, and camera.
· Time saved with AI leads to more creative work
· Seeking: A single source of truth
· TLDR; Get on social, try AI, and align your systems.
· More human marketing, powered by robots
ChatGPT is a revolutionary addition to the world since its introduction in 2022. A big shift in the sector of information gathering and processing happened because of this chatbot. What is the story of ChatGPT? How is the bot responding to prompts and generating contents? Swipe through these slides prepared by Expeed Software, a web development company regarding the development and technical intricacies of ChatGPT!
Product Design Trends in 2024 | Teenage EngineeringsPixeldarts
The realm of product design is a constantly changing environment where technology and style intersect. Every year introduces fresh challenges and exciting trends that mold the future of this captivating art form. In this piece, we delve into the significant trends set to influence the look and functionality of product design in the year 2024.
How Race, Age and Gender Shape Attitudes Towards Mental HealthThinkNow
Mental health has been in the news quite a bit lately. Dozens of U.S. states are currently suing Meta for contributing to the youth mental health crisis by inserting addictive features into their products, while the U.S. Surgeon General is touring the nation to bring awareness to the growing epidemic of loneliness and isolation. The country has endured periods of low national morale, such as in the 1970s when high inflation and the energy crisis worsened public sentiment following the Vietnam War. The current mood, however, feels different. Gallup recently reported that national mental health is at an all-time low, with few bright spots to lift spirits.
To better understand how Americans are feeling and their attitudes towards mental health in general, ThinkNow conducted a nationally representative quantitative survey of 1,500 respondents and found some interesting differences among ethnic, age and gender groups.
Technology
For example, 52% agree that technology and social media have a negative impact on mental health, but when broken out by race, 61% of Whites felt technology had a negative effect, and only 48% of Hispanics thought it did.
While technology has helped us keep in touch with friends and family in faraway places, it appears to have degraded our ability to connect in person. Staying connected online is a double-edged sword since the same news feed that brings us pictures of the grandkids and fluffy kittens also feeds us news about the wars in Israel and Ukraine, the dysfunction in Washington, the latest mass shooting and the climate crisis.
Hispanics may have a built-in defense against the isolation technology breeds, owing to their large, multigenerational households, strong social support systems, and tendency to use social media to stay connected with relatives abroad.
Age and Gender
When asked how individuals rate their mental health, men rate it higher than women by 11 percentage points, and Baby Boomers rank it highest at 83%, saying it’s good or excellent vs. 57% of Gen Z saying the same.
Gen Z spends the most amount of time on social media, so the notion that social media negatively affects mental health appears to be correlated. Unfortunately, Gen Z is also the generation that’s least comfortable discussing mental health concerns with healthcare professionals. Only 40% of them state they’re comfortable discussing their issues with a professional compared to 60% of Millennials and 65% of Boomers.
Race Affects Attitudes
As seen in previous research conducted by ThinkNow, Asian Americans lag other groups when it comes to awareness of mental health issues. Twenty-four percent of Asian Americans believe that having a mental health issue is a sign of weakness compared to the 16% average for all groups. Asians are also considerably less likely to be aware of mental health services in their communities (42% vs. 55%) and most likely to seek out information on social media (51% vs. 35%).
AI Trends in Creative Operations 2024 by Artwork Flow.pdfmarketingartwork
This article is all about what AI trends will emerge in the field of creative operations in 2024. All the marketers and brand builders should be aware of these trends for their further use and save themselves some time!
A report by thenetworkone and Kurio.
The contributing experts and agencies are (in an alphabetical order): Sylwia Rytel, Social Media Supervisor, 180heartbeats + JUNG v MATT (PL), Sharlene Jenner, Vice President - Director of Engagement Strategy, Abelson Taylor (USA), Alex Casanovas, Digital Director, Atrevia (ES), Dora Beilin, Senior Social Strategist, Barrett Hoffher (USA), Min Seo, Campaign Director, Brand New Agency (KR), Deshé M. Gully, Associate Strategist, Day One Agency (USA), Francesca Trevisan, Strategist, Different (IT), Trevor Crossman, CX and Digital Transformation Director; Olivia Hussey, Strategic Planner; Simi Srinarula, Social Media Manager, The Hallway (AUS), James Hebbert, Managing Director, Hylink (CN / UK), Mundy Álvarez, Planning Director; Pedro Rojas, Social Media Manager; Pancho González, CCO, Inbrax (CH), Oana Oprea, Head of Digital Planning, Jam Session Agency (RO), Amy Bottrill, Social Account Director, Launch (UK), Gaby Arriaga, Founder, Leonardo1452 (MX), Shantesh S Row, Creative Director, Liwa (UAE), Rajesh Mehta, Chief Strategy Officer; Dhruv Gaur, Digital Planning Lead; Leonie Mergulhao, Account Supervisor - Social Media & PR, Medulla (IN), Aurelija Plioplytė, Head of Digital & Social, Not Perfect (LI), Daiana Khaidargaliyeva, Account Manager, Osaka Labs (UK / USA), Stefanie Söhnchen, Vice President Digital, PIABO Communications (DE), Elisabeth Winiartati, Managing Consultant, Head of Global Integrated Communications; Lydia Aprina, Account Manager, Integrated Marketing and Communications; Nita Prabowo, Account Manager, Integrated Marketing and Communications; Okhi, Web Developer, PNTR Group (ID), Kei Obusan, Insights Director; Daffi Ranandi, Insights Manager, Radarr (SG), Gautam Reghunath, Co-founder & CEO, Talented (IN), Donagh Humphreys, Head of Social and Digital Innovation, THINKHOUSE (IRE), Sarah Yim, Strategy Director, Zulu Alpha Kilo (CA).
Trends In Paid Search: Navigating The Digital Landscape In 2024Search Engine Journal
The search marketing landscape is evolving rapidly with new technologies, and professionals, like you, rely on innovative paid search strategies to meet changing demands.
It’s important that you’re ready to implement new strategies in 2024.
Check this out and learn the top trends in paid search advertising that are expected to gain traction, so you can drive higher ROI more efficiently in 2024.
You’ll learn:
- The latest trends in AI and automation, and what this means for an evolving paid search ecosystem.
- New developments in privacy and data regulation.
- Emerging ad formats that are expected to make an impact next year.
Watch Sreekant Lanka from iQuanti and Irina Klein from OneMain Financial as they dive into the future of paid search and explore the trends, strategies, and technologies that will shape the search marketing landscape.
If you’re looking to assess your paid search strategy and design an industry-aligned plan for 2024, then this webinar is for you.
5 Public speaking tips from TED - Visualized summarySpeakerHub
From their humble beginnings in 1984, TED has grown into the world’s most powerful amplifier for speakers and thought-leaders to share their ideas. They have over 2,400 filmed talks (not including the 30,000+ TEDx videos) freely available online, and have hosted over 17,500 events around the world.
With over one billion views in a year, it’s no wonder that so many speakers are looking to TED for ideas on how to share their message more effectively.
The article “5 Public-Speaking Tips TED Gives Its Speakers”, by Carmine Gallo for Forbes, gives speakers five practical ways to connect with their audience, and effectively share their ideas on stage.
Whether you are gearing up to get on a TED stage yourself, or just want to master the skills that so many of their speakers possess, these tips and quotes from Chris Anderson, the TED Talks Curator, will encourage you to make the most impactful impression on your audience.
See the full article and more summaries like this on SpeakerHub here: https://speakerhub.com/blog/5-presentation-tips-ted-gives-its-speakers
See the original article on Forbes here:
http://www.forbes.com/forbes/welcome/?toURL=http://www.forbes.com/sites/carminegallo/2016/05/06/5-public-speaking-tips-ted-gives-its-speakers/&refURL=&referrer=#5c07a8221d9b
ChatGPT and the Future of Work - Clark Boyd Clark Boyd
Everyone is in agreement that ChatGPT (and other generative AI tools) will shape the future of work. Yet there is little consensus on exactly how, when, and to what extent this technology will change our world.
Businesses that extract maximum value from ChatGPT will use it as a collaborative tool for everything from brainstorming to technical maintenance.
For individuals, now is the time to pinpoint the skills the future professional will need to thrive in the AI age.
Check out this presentation to understand what ChatGPT is, how it will shape the future of work, and how you can prepare to take advantage.
A brief introduction to DataScience with explaining of the concepts, algorithms, machine learning, supervised and unsupervised learning, clustering, statistics, data preprocessing, real-world applications etc.
It's part of a Data Science Corner Campaign where I will be discussing the fundamentals of DataScience, AIML, Statistics etc.
Time Management & Productivity - Best PracticesVit Horky
Here's my presentation on by proven best practices how to manage your work time effectively and how to improve your productivity. It includes practical tips and how to use tools such as Slack, Google Apps, Hubspot, Google Calendar, Gmail and others.
The six step guide to practical project managementMindGenius
The six step guide to practical project management
If you think managing projects is too difficult, think again.
We’ve stripped back project management processes to the
basics – to make it quicker and easier, without sacrificing
the vital ingredients for success.
“If you’re looking for some real-world guidance, then The Six Step Guide to Practical Project Management will help.”
Dr Andrew Makar, Tactical Project Management
2024 State of Marketing Report – by HubspotMarius Sescu
https://www.hubspot.com/state-of-marketing
· Scaling relationships and proving ROI
· Social media is the place for search, sales, and service
· Authentic influencer partnerships fuel brand growth
· The strongest connections happen via call, click, chat, and camera.
· Time saved with AI leads to more creative work
· Seeking: A single source of truth
· TLDR; Get on social, try AI, and align your systems.
· More human marketing, powered by robots
ChatGPT is a revolutionary addition to the world since its introduction in 2022. A big shift in the sector of information gathering and processing happened because of this chatbot. What is the story of ChatGPT? How is the bot responding to prompts and generating contents? Swipe through these slides prepared by Expeed Software, a web development company regarding the development and technical intricacies of ChatGPT!
Product Design Trends in 2024 | Teenage EngineeringsPixeldarts
The realm of product design is a constantly changing environment where technology and style intersect. Every year introduces fresh challenges and exciting trends that mold the future of this captivating art form. In this piece, we delve into the significant trends set to influence the look and functionality of product design in the year 2024.
How Race, Age and Gender Shape Attitudes Towards Mental HealthThinkNow
Mental health has been in the news quite a bit lately. Dozens of U.S. states are currently suing Meta for contributing to the youth mental health crisis by inserting addictive features into their products, while the U.S. Surgeon General is touring the nation to bring awareness to the growing epidemic of loneliness and isolation. The country has endured periods of low national morale, such as in the 1970s when high inflation and the energy crisis worsened public sentiment following the Vietnam War. The current mood, however, feels different. Gallup recently reported that national mental health is at an all-time low, with few bright spots to lift spirits.
To better understand how Americans are feeling and their attitudes towards mental health in general, ThinkNow conducted a nationally representative quantitative survey of 1,500 respondents and found some interesting differences among ethnic, age and gender groups.
Technology
For example, 52% agree that technology and social media have a negative impact on mental health, but when broken out by race, 61% of Whites felt technology had a negative effect, and only 48% of Hispanics thought it did.
While technology has helped us keep in touch with friends and family in faraway places, it appears to have degraded our ability to connect in person. Staying connected online is a double-edged sword since the same news feed that brings us pictures of the grandkids and fluffy kittens also feeds us news about the wars in Israel and Ukraine, the dysfunction in Washington, the latest mass shooting and the climate crisis.
Hispanics may have a built-in defense against the isolation technology breeds, owing to their large, multigenerational households, strong social support systems, and tendency to use social media to stay connected with relatives abroad.
Age and Gender
When asked how individuals rate their mental health, men rate it higher than women by 11 percentage points, and Baby Boomers rank it highest at 83%, saying it’s good or excellent vs. 57% of Gen Z saying the same.
Gen Z spends the most amount of time on social media, so the notion that social media negatively affects mental health appears to be correlated. Unfortunately, Gen Z is also the generation that’s least comfortable discussing mental health concerns with healthcare professionals. Only 40% of them state they’re comfortable discussing their issues with a professional compared to 60% of Millennials and 65% of Boomers.
Race Affects Attitudes
As seen in previous research conducted by ThinkNow, Asian Americans lag other groups when it comes to awareness of mental health issues. Twenty-four percent of Asian Americans believe that having a mental health issue is a sign of weakness compared to the 16% average for all groups. Asians are also considerably less likely to be aware of mental health services in their communities (42% vs. 55%) and most likely to seek out information on social media (51% vs. 35%).
AI Trends in Creative Operations 2024 by Artwork Flow.pdfmarketingartwork
This article is all about what AI trends will emerge in the field of creative operations in 2024. All the marketers and brand builders should be aware of these trends for their further use and save themselves some time!
A report by thenetworkone and Kurio.
The contributing experts and agencies are (in an alphabetical order): Sylwia Rytel, Social Media Supervisor, 180heartbeats + JUNG v MATT (PL), Sharlene Jenner, Vice President - Director of Engagement Strategy, Abelson Taylor (USA), Alex Casanovas, Digital Director, Atrevia (ES), Dora Beilin, Senior Social Strategist, Barrett Hoffher (USA), Min Seo, Campaign Director, Brand New Agency (KR), Deshé M. Gully, Associate Strategist, Day One Agency (USA), Francesca Trevisan, Strategist, Different (IT), Trevor Crossman, CX and Digital Transformation Director; Olivia Hussey, Strategic Planner; Simi Srinarula, Social Media Manager, The Hallway (AUS), James Hebbert, Managing Director, Hylink (CN / UK), Mundy Álvarez, Planning Director; Pedro Rojas, Social Media Manager; Pancho González, CCO, Inbrax (CH), Oana Oprea, Head of Digital Planning, Jam Session Agency (RO), Amy Bottrill, Social Account Director, Launch (UK), Gaby Arriaga, Founder, Leonardo1452 (MX), Shantesh S Row, Creative Director, Liwa (UAE), Rajesh Mehta, Chief Strategy Officer; Dhruv Gaur, Digital Planning Lead; Leonie Mergulhao, Account Supervisor - Social Media & PR, Medulla (IN), Aurelija Plioplytė, Head of Digital & Social, Not Perfect (LI), Daiana Khaidargaliyeva, Account Manager, Osaka Labs (UK / USA), Stefanie Söhnchen, Vice President Digital, PIABO Communications (DE), Elisabeth Winiartati, Managing Consultant, Head of Global Integrated Communications; Lydia Aprina, Account Manager, Integrated Marketing and Communications; Nita Prabowo, Account Manager, Integrated Marketing and Communications; Okhi, Web Developer, PNTR Group (ID), Kei Obusan, Insights Director; Daffi Ranandi, Insights Manager, Radarr (SG), Gautam Reghunath, Co-founder & CEO, Talented (IN), Donagh Humphreys, Head of Social and Digital Innovation, THINKHOUSE (IRE), Sarah Yim, Strategy Director, Zulu Alpha Kilo (CA).
Trends In Paid Search: Navigating The Digital Landscape In 2024Search Engine Journal
The search marketing landscape is evolving rapidly with new technologies, and professionals, like you, rely on innovative paid search strategies to meet changing demands.
It’s important that you’re ready to implement new strategies in 2024.
Check this out and learn the top trends in paid search advertising that are expected to gain traction, so you can drive higher ROI more efficiently in 2024.
You’ll learn:
- The latest trends in AI and automation, and what this means for an evolving paid search ecosystem.
- New developments in privacy and data regulation.
- Emerging ad formats that are expected to make an impact next year.
Watch Sreekant Lanka from iQuanti and Irina Klein from OneMain Financial as they dive into the future of paid search and explore the trends, strategies, and technologies that will shape the search marketing landscape.
If you’re looking to assess your paid search strategy and design an industry-aligned plan for 2024, then this webinar is for you.
5 Public speaking tips from TED - Visualized summarySpeakerHub
From their humble beginnings in 1984, TED has grown into the world’s most powerful amplifier for speakers and thought-leaders to share their ideas. They have over 2,400 filmed talks (not including the 30,000+ TEDx videos) freely available online, and have hosted over 17,500 events around the world.
With over one billion views in a year, it’s no wonder that so many speakers are looking to TED for ideas on how to share their message more effectively.
The article “5 Public-Speaking Tips TED Gives Its Speakers”, by Carmine Gallo for Forbes, gives speakers five practical ways to connect with their audience, and effectively share their ideas on stage.
Whether you are gearing up to get on a TED stage yourself, or just want to master the skills that so many of their speakers possess, these tips and quotes from Chris Anderson, the TED Talks Curator, will encourage you to make the most impactful impression on your audience.
See the full article and more summaries like this on SpeakerHub here: https://speakerhub.com/blog/5-presentation-tips-ted-gives-its-speakers
See the original article on Forbes here:
http://www.forbes.com/forbes/welcome/?toURL=http://www.forbes.com/sites/carminegallo/2016/05/06/5-public-speaking-tips-ted-gives-its-speakers/&refURL=&referrer=#5c07a8221d9b
ChatGPT and the Future of Work - Clark Boyd Clark Boyd
Everyone is in agreement that ChatGPT (and other generative AI tools) will shape the future of work. Yet there is little consensus on exactly how, when, and to what extent this technology will change our world.
Businesses that extract maximum value from ChatGPT will use it as a collaborative tool for everything from brainstorming to technical maintenance.
For individuals, now is the time to pinpoint the skills the future professional will need to thrive in the AI age.
Check out this presentation to understand what ChatGPT is, how it will shape the future of work, and how you can prepare to take advantage.
A brief introduction to DataScience with explaining of the concepts, algorithms, machine learning, supervised and unsupervised learning, clustering, statistics, data preprocessing, real-world applications etc.
It's part of a Data Science Corner Campaign where I will be discussing the fundamentals of DataScience, AIML, Statistics etc.
Time Management & Productivity - Best PracticesVit Horky
Here's my presentation on by proven best practices how to manage your work time effectively and how to improve your productivity. It includes practical tips and how to use tools such as Slack, Google Apps, Hubspot, Google Calendar, Gmail and others.
The six step guide to practical project managementMindGenius
The six step guide to practical project management
If you think managing projects is too difficult, think again.
We’ve stripped back project management processes to the
basics – to make it quicker and easier, without sacrificing
the vital ingredients for success.
“If you’re looking for some real-world guidance, then The Six Step Guide to Practical Project Management will help.”
Dr Andrew Makar, Tactical Project Management
Beginners Guide to TikTok for Search - Rachel Pearson - We are Tilt __ Bright...
基于Surf与光流法的增强现实跟踪注册
1. Computer Engineering and Applications计算机工程与应用2015,51(3)
1 引言
增强现实(Augmented Reality,AR)是通过电脑技
术将虚拟的物体实时地叠加到真实的场景之中的一种
技术。增强现实具有三大特点:虚实结合、实时交互和
三维注册[1]
,其中三维注册是增强现实的核心技术,已成
为当今研究的热点之一。当前三维注册技术一般可以
分为:基于特殊标识的注册和基于自然特征的注册[2]
。
由于基于特殊标识的注册方法依赖人为标识,使用起来
颇为不便,从而限制了其在现实中的应用范围[3]
。近年
来,随着计算机图形学和计算机视觉技术的发展,基于
标识平面的自然特征注册方法已可以满足大部分应用
需求,它利用场景中的物体作为标识平面,因而不受场
合的限制,已成为增强现实发展的趋势。
目前,大多数基于自然特征的注册方法都是基于特
征点的跟踪与匹配策略,其中特征点的提取与匹配需要
大量的运算时间,这样就会对系统三维注册的速度与精
度造成一定的影响,甚至造成注册错误。
SURF[4]
特征匹配算法是目前比较流行的特征匹配
算法之一,与较成熟的 SIFT[5]
算法相比,其在保持 SIFT
仿射、尺度不变性等优点的同时,提取与匹配速度得到
了较大提高[6]
。光流法是通过跟踪特征点坐标的方式来
对移动区域进行跟踪,运算简单快速,但持续的跟踪会
积累一定的误差,跟踪时间过长可能会造成跟踪失败[7]
。
针对以上分析,本文提出一种基于 SURF 与光流法
相结合的局部跟踪注册方法,采用光流法对移动对象
(标识平面)进行跟踪,以减小特征点提取与匹配的区
域,使用更新光流策略解决光流长时间跟踪容易失败的
问题;利用 SURF 算法对移动对象区域进行特征点的提
基于 SURF 与光流法的增强现实跟踪注册
张志禹,刘耀阳
ZHANG Zhiyu, LIU Yaoyang
西安理工大学 自动化与信息工程学院,西安 710048
Faculty of Automation and Information Engineering, Xi’an University of Technology, Xi’an 710048, China
ZHANG Zhiyu, LIU Yaoyang. Tracking and AR registration based on SURF and optical flow method. Computer
Engineering and Applications, 2015, 51(3):166-170.
Abstract:A tracking and registration method based on SURF and optical flow in the AR is proposed. The moving object
region is tracked by the optical flow method. This paper extracts and matches the features of the region with SURF because
the algorithm maintains advantages of affine invariance, scale invariance and fast computing speed. The final registration
matrix is calculated using the homographies between adjacent frames. This method reduces the computational time deeply
while the accuracy of the registration unchanges. Convinced by experimental results, this approach can work at almost real
time and achieves accurate registration, and can keep a good robustness in some environment changes.
Key words:region-based tracking; Speeded Up Robust Features(SURF)feature extraction; optical flow method; homog-
raphy; 3D-registration
摘 要:提出一种基于 SURF 与光流法相结合的增强现实局部跟踪注册方法。采用光流法对移动对象区域进行跟
踪,利用 SURF 算法仿射、尺度不变性及运算速度快的优点对该区域进行特征提取与匹配,利用相邻帧之间特征点的
匹配关系求得三维注册矩阵,在保持注册精确性的同时降低了系统运算时间。实验结果表明该方法达到了实时跟
踪与准确注册的效果,并且在环境变化时保持了较好的鲁棒性。
关键词:局部跟踪;加速稳健特征(SURF)特征提取;光流法;单应性矩阵;三维注册
文献标志码:A 中图分类号:TP391 doi:10.3778/j.issn.1002-8331.1303-0339
作者简介:张志禹(1966—),男,博士,教授,研究领域为数字信号处理、小波变换;刘耀阳(1987—),男,硕士研究生,研究领域为
增强现实、嵌入式系统。E-mail:liuyaoyang815@126.com
收稿日期:2013-03-22 修回日期:2013-05-07 文章编号:1002-8331(2015)03-0166-05
CNKI网络优先出版:2013-06-18,http://www.cnki.net/kcms/detail/11.2127.TP.20130618.1601.013.html
166
2. 2015,51(3)
取与匹配,得到相邻帧之间的单应性关系,进而求出三
维注册矩阵并完成注册。
为快速匹配及跟踪移动对象,首先对输入的视频图
像进行色彩转换,按照公式(1)[8]
转换为灰度图,以降低
计算维度,增加运算效率。
I = 0.299 ´ R + 0.587 ´ G + 0.114 ´ B (1)
2 SURF 特征提取
SURF 特征提取的主要步骤包括:(1)特征点提取,
首先建立积分图像,然后利用盒子滤波器进行图像滤
波,利用 Hessian 矩阵确定候选点,然后进行非极大值抑
制,得到极大值点;(2)特征点描述,在特征点各子区域
上计算 Haar小波响应,并记录其中 4种以生成 4×4×4=64
维特征描述符[9]
。
2.1 特征点提取
(1)建立积分图像
建立积分图像的目的在于可以利用查表(look-up
table)的方式快速计算图像中任意矩形区域的像素值总
和,以便在进行滤波运算时,当处理的区域面积很大时,
可以降低运算量和处理时间,其计算方法如公式(2)。
IΣ(xy)= åi = 0
i x
åj = 0
j y
I(xy) (2)
(2)建立图像的尺度空间
SURF 尺度空间是在 SIFT 建立金字塔尺度空间的
概念基础上建立的,以固定原始图像大小,改变 Hessian
检测算子的滤波器大小来实现尺度空间的效果。采用
三个倍频,且每个倍频内有四个不同尺度的 Hessian 检
测算子。如图 1 所示,图中(a)为 SIFT 尺度空间建立时,
滤波器大小不变改变原图尺寸,(b)为 SURF 尺度空间
建立时原图尺寸不变但改变滤波器大小。
(3)海森矩阵(Hessian)特征检测
假设函数 f (xy) ,海森矩阵 H 是由函数 f 的偏导
数组成,如公式(3)所示,在不同的尺度空间下所求的海
森矩阵如公式(4),其中 Gyy(xyδ) 为高斯核函数对 y
的二次偏微分,其余类推。
H( f (xy)) =
é
ë
ê
ê
ê
êê
ê
ù
û
ú
ú
ú
úú
ú
¶2
f
¶x2
¶2
f
¶x¶y
¶2
f
¶x¶y
¶2
f
¶y2
(3)
H(xyδ) =
æ
è
çç
ö
ø
÷÷
Gxx(xyδ)´ I(xy) Gxy(xyδ)´ I(xy)
Gxy(xyδ)´I(xy) Gyy(xyδ)´I(xy)
(4)
为了图像与高斯二阶差分运算,将离散信号用滤波
器加以简化,将其运算算子取近似值,对于在不同尺度
空间的海森矩阵如公式(5),其中 0.9 为一常数,主要为
补偿取近似值后的误差,最后对每一尺度每个像素进行
运算,当 Happrox > 1 时则判定该点为兴趣点。
det(Happrox) = Dxx Dyy -(0.9 ´ Dxy)2
(5)
(4)特征点定位
兴趣点确定后,接下来就以这些兴趣点搜索确定特
征点,以图 2 为例,若尺度空间中存在一个 X 点为周围
26 个点中的最大值(上一层 9 个邻近点、同一层 8 个邻近
点与下一层 9 个邻近点),则该点即判定为特征点。
2.2 特征点描述
(1)计算特征点方向
为保持旋转不变性,首先以特征点为圆心取半径大
小为 6δ(δ为特征点所在尺度值)的圆形区域,对 δ 每个
点计算一阶 Haar 小波响应(Haar 小波边长为 4δ),并进
行高斯加权,其一阶导数可表示运算区域与其方向的梯
度。再以圆心角(60°)扇形窗口绕着特征点扫描,并根
据每个扫描角度,统计扇形窗口内的一阶导数值(dx 与
dy)的矢量和,以扇形区域内最大值的扫描角度作为其
特征的主要方向。如图 3 所示,斑点部分为 Haar 小波响
应值(dx 与 dy),灰色扇形为扫描窗口,箭头长度为经过
矢量和后的大小,箭头方向则表示为特征点方向。
(2)基于 Haar小波响应的描述符
特征点描述的建立是以特征点为中心建立一个边
长为 20δ大小的正方形区域,并在区域内以 5δ为边长大
小划分子区域。在各个子区域中,计算以边长为 2δ大小
的一阶 Haar 小波响应(dx 与 dy),以最左上角第一个像
Scale
Scale
(a)SIFT 建立尺度空间图 (b)SURF 建立尺度空间图
图 1 SIFT 与 SURF 金字塔尺度空间建立示意图
Scale
图 2 极值搜索示意图
dx
dy
图 3 主方向示意图
O
张志禹,刘耀阳:基于 SURF 与光流法的增强现实跟踪注册 167
3. Computer Engineering and Applications计算机工程与应用2015,51(3)
素点起,每隔 δ 像素的距离进行一次运算,因此每个 Haar
小波在每个子区域内共计算 25 次,如图 4 所示。
每个子区域分别计算出 Σdx、Σdy、Σ|dx| 与 Σ|dy| 四
个矢量,这 16 个子区域的特征矢量便可以形成一个描
述该特征点的 4 ´ 4 ´ 4 = 64 维度的特征描述子。
3 移动对象跟踪与特征匹配
3.1 移动对象跟踪
在特征匹配时,若对匹配图像全局提取特征点再与
目标图像特征点一一匹配,运算时间相对较长,进而会
影响注册的实时性。若缩小图像大小,匹配时间可相应
缩短,但这样所获得特征点会变少,不利于后续跟踪匹
配。由于光流法对小幅度的移动有很好的跟踪效果,故
结合光流法(本文采用金字塔 L-K光流法)来跟踪移动对
象区域,这样既可以缩短匹配时间,又不会减少匹配点。
而对于较大幅度的移动,采用扩充边界的方法来更
新跟踪区域。其计算方法如图 5 所示,取上一帧对象上
特征点中 X 与 Y 坐标最大值及最小值,二点可绘出一个
矩形框,此矩形区域即为新的跟踪区域。其中(a)为上
一帧:虚框内为跟踪区域,虚框内四边形为移动对象的
轮廓,(b)为当前帧:仅在该区域检测特征点。
3.2 特征点匹配
对当前帧的跟踪区域进行 SURF 特征点检测,首先
要保证该区域有足够数量的高质量特征点[10]
,对于高质
量特征点的判断是:
hi > H (6)
式中 hi 是由 SURF 特征提取得到的 Hessian 值,阈值 H
的合理值一般为 1 000。特征点选取之后,便可以与上
一帧的特征点进行匹配,特征匹配采用文献[4]的方法
来完成。由于对象移动或噪声等因素的存在[11]
,误匹配
点难以避免,采用 RANSAC 算法[12]
去除匹配错误的特
征点。
3.3 基于单应性的三维注册矩阵计算
对位于世界坐标系的一点 Q =(XYZ1)T
与其在
成像平面上的投影 q =(xy1)T
之间的关系可表示为公
式(7)。
q = λKMQ = λK
æ
è
ç
ö
ø
÷
R1 R2 R3 T
0 0 0 1
Q (7)
其中 M 为待求的三维注册矩阵,λ 是比例因子,K 是
摄像机的内参矩阵(本系统通过摄像机定标来获取),
(R1R2R3) 和 T 分别是三维注册矩阵 M 的 3个旋转分量
和一个平移分量[13]
。在对象坐标系下时,ZW = 0,公式(7)
可转化为:
é
ë
ê
ê
ù
û
ú
ú
x
y
1
= λK
æ
è
ç
ö
ø
÷
R1 R2 R3 T
0 0 0 1
é
ë
ê
ê
êê
ù
û
ú
ú
úú
X
Y
0
1
=
λK æ
è
ç
ö
ø
÷
R1 R2 T
0 0 1
é
ë
ê
ê
ù
û
ú
ú
X
Y
1
= HW
é
ë
ê
ê
ù
û
ú
ú
X
Y
1
(8)
公式(8)中矩阵 HW 为对象与二维图像之间的单应
性矩阵。在已知比例因子 λ、单应性矩阵 HW 和摄像机
内参矩阵 K 的情况下,设 HW 的列向量分别为 H1、H2、
H3 ,可以求得:
R1 = 1
λ
K-1
H1
K-1
H1
(9)
R2 = 1
λ
K-1
H2
K-1
H2
(10)
T = 1
λ
K-1
H3
K-1
H3
(11)
再根据正交性,可以求得 R3 = R2 ´ R1 ,进而完成三
维注册。
定义 H
j
i 为第 j 帧图像与第 j - 1 帧图像间的单应
性矩阵,则:
(xjyj1)T
= H
j
i (xj - 1yj - 11)T
(12)
由此可得第 j 帧图像与初始帧图像间的单应性矩阵:
H
j
i H
j - 1
i H 2
i H1
i (13)
利用公式(8)进而可求得第 j 帧图像与目标对象间
的单应性矩阵:
H
j
w = H
j
i H
j - 1
i H 2
i H1
i H 0
w (14)
式中 H 0
w 代表标识平面与初始帧图像间的初始单应性
矩阵,由公式(14)可知,若获取了 H 0
w 和 H
j
i ,便可以求
得 H
j
w ,以下介绍获取 H 0
w 和 H
j
i 的过程。
在初始帧情况下,定义对象坐标系 z = 0 ,并把 (xy)
的位置归一化在以平面标识中心为坐标原点的坐标系
Σdx
Σdy
Σ|dx|
Σ|dy|
dydx
图 4 特征点描述示意图
(a)上一帧搜索图 (b)当前帧搜索图
图 5 搜索区示意图
168
5. Computer Engineering and Applications计算机工程与应用2015,51(3)
用更新光流法跟踪移动对象区域,保证了跟踪的稳定性
与精确性,采用 SURF 特征提取与匹配算法在对旋转、
尺度缩放、亮度、视角及仿射等保持不变性的同时,确保
了运算速度,最后采用基于单应性的注册矩阵的计算,
较好地保证了注册的准确性。实验结果表明,本文方法
较好地满足了基于自然特征跟踪注册方法对实时性和
精确度的要求。
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